Cross-polarization in liquid-state NMR has been only infrequently applied to multidimensional correlation experiments. It finds special utility, however, in analytes bearing multiple 1H and 19F nuclei, either in heteronuclear total correlation spectroscopy (TOCSY), or as a means of efficiently utilizing the thermal polarization of both abundant, high-gamma nuclei. A significant limitation to that application had been the restricted spectral window over which an effective spin-lock could be applied with typical composite sequences; this window comprises only a small portion of the 19F spectral window that is generally of interest. The use of matched BURBOP pulses to induce a spin lock significantly extends the effective window and renders cross-polarization much more applicable for polyfluorinated organic molecules. In this work, a 19F-1H hetero-TOCSY spanning nearly 50 kHz in the 19F dimension is demonstrated. In addition, the use of 19F-1H cross-polarization to enhance the sensitivity of a 1H-13C ASAP-HSQC experiment is demonstrated. The magnitude of this enhancement depends on the pathway of scalar coupling between 19F and 1H nuclei of interest; in cases where the coupling is large, and transferred over relatively few bonds, ca. 10% enhancement can be observed.

Applications of broadband 19F-1H cross-polarization in NMR spectroscopy: Hetero-TOCSY and ASAP-HSQC

2019 Fall National Meeting

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